Quantitative model for current-voltage characteristics of metal point contacts on silicon rectifying junctions

Abstract

Metal point contacts on semiconductors result in rectifying contacts whose current-voltage characteristics do not obey the Schottky diode formula. However, the curves under loads varying from 20 to 100 g have been found to be described by a constriction resistance in series with a rectifying device whose law is of the form I=I0 (exp αV−1). The α exponent varies with load and would correspond, as compared to a Schottky diode, to high values of the idealization factor. A brief synthesis of the existing surface mechanic models shows that the real area of contact Ar must be proportional to the load. This is checked with the classical formulation for constriction resistances and so we obtain the measure of Ar . These results allow us to conclude that the deformations of silicon at the interface are mostly plastic. A great number of dislocations appear and cause the existence of many traps which are responsible for a tunneling effect through the metal–semiconductor barrier. This enables us to explain the low values of α and to determine the barrier height. Furthermore, we obtain the formula relating α and I0 to Ar and a plot of Ar versus the load agrees well with the mechanical theory.